1. Field
Disclosed herein is a current sensor arrangement for measurement of currents in a primary conductor over a wide measurement range.
2. Description of Related Art
On the one hand, so-called direct-mapping current sensors are known for non-contacting, and therefore electrically floating measurement of the level of an electric current in a conductor, which sensors sense the magnetic flux caused by the current, for example by means of a Hall sensor in a slotted magnetic circuit, and produce a signal which is proportional to the current level. These sensors are highly cost-effective, but are relatively inaccurate. Direct-mapping current sensors are so-called open-loop current sensors which do not contain a closed control loop.
Furthermore, so-called closed-loop current sensors are known, in which a closed control loop is used to continuously produce a magnetic opposing field of the same magnitude as the current to be measured as a result of which complete magnetic-field compensation occurs, and the magnitude of the current to be measured can be deduced from the parameters to produce the opposing field. Closed-loop current sensors therefore belong to the class of compensation current sensors.
One special type of compensation current sensors which, however, do not contain a closed control loop is flux gate sensors which are described, for example, in the document DE 42 29 948. Since current sensors such as these avoid any hysteresis error, they are suitable for precise current measurement over a wide dynamic range from a few milliamperes up to about one kiloampere.
Flux gate sensors do not allow continuous current measurement, but the output signal of the sensor is a periodic signal which is sampled at specific sampling times. The sample values represent the current in the primary conductor (primary current) at the discrete sampling times.
In the case of the known flux gate sensor, the sampling frequency is predetermined by the oscillation frequency of the sensor (sensor frequency) and in consequence by the inductance of the sensor arrangement. The inductance is frequently chosen to be high, in order to make the sensor less sensitive to disturbances, as a result of which, however, the sensor frequency is relatively low. Although the inductance could be reduced, and the sensor frequency increased, by using small coils and coil cores, this is frequently not feasible because of the increased susceptibility of relatively small cores to disturbance. The actual design of conventional flux gate sensors is therefore always a compromise between the contradictory design aims of high sensor frequency (and therefore high time resolution) on the one hand and high inductance (because of the reduced susceptibility to disturbances) on the other hand. The sensor design is defined for a specific application and cannot be changed during operation.
One problem with the known flux gate sensors is the high maximum current draw resulting from the periodic complete remagnetization of the magnet system of the flux gate sensor, which results in the use of flux gate sensors being of little interest, for financial reasons, for many applications.
A further problem can occur when the frequency of the primary current is similar to or equal to the sensor frequency, or is an integer multiple of it. Beatings can then be observed in the sampled output signal of the sensor as a result of aliasing effects, and these beatings are in a frequency range which may be important for the current measurement. These beatings obviously interfere with the measurement. This interference may be of such an extent that worthwhile current measurement is impossible in some cases, thus greatly restricting the practical field of application of the current sensor.